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authorLinus Torvalds <torvalds@linux-foundation.org>2020-08-14 15:22:43 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-14 15:22:43 -0700
commit5848dc5b1b76d83599dcec1b39f188a7cbdca7e2 (patch)
tree740d7bd1ae3c67665ff0d602e1ccfea013609264 /kernel
parenta85ffd59bd362d6c2e456e7f523b091830cd5454 (diff)
downloadlinux-5848dc5b1b76d83599dcec1b39f188a7cbdca7e2.tar.bz2
dma-debug: remove debug_dma_assert_idle() function
This remoes the code from the COW path to call debug_dma_assert_idle(), which was added many years ago. Google shows that it hasn't caught anything in the 6+ years we've had it apart from a false positive, and Hugh just noticed how it had a very unfortunate spinlock serialization in the COW path. He fixed that issue the previous commit (a85ffd59bd36: "dma-debug: fix debug_dma_assert_idle(), use rcu_read_lock()"), but let's see if anybody even notices when we remove this function entirely. NOTE! We keep the dma tracking infrastructure that was added by the commit that introduced it. Partly to make it easier to resurrect this debug code if we ever deside to, and partly because that tracking by pfn and offset looks quite reasonable. The problem with this debug code was simply that it was expensive and didn't seem worth it, not that it was wrong per se. Acked-by: Dan Williams <dan.j.williams@intel.com> Acked-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/dma/Kconfig5
-rw-r--r--kernel/dma/debug.c46
2 files changed, 1 insertions, 50 deletions
diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index f4770fcfa62b..5732b2b3ef17 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -186,11 +186,6 @@ config DMA_API_DEBUG
drivers like double-freeing of DMA mappings or freeing mappings that
were never allocated.
- This also attempts to catch cases where a page owned by DMA is
- accessed by the cpu in a way that could cause data corruption. For
- example, this enables cow_user_page() to check that the source page is
- not undergoing DMA.
-
This option causes a performance degradation. Use only if you want to
debug device drivers and dma interactions.
diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index 6f4f4b9d2d03..8e9f7b301c6d 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -448,9 +448,6 @@ void debug_dma_dump_mappings(struct device *dev)
* dma_active_cacheline entry to track per event. dma_map_sg(), on the
* other hand, consumes a single dma_debug_entry, but inserts 'nents'
* entries into the tree.
- *
- * At any time debug_dma_assert_idle() can be called to trigger a
- * warning if any cachelines in the given page are in the active set.
*/
static RADIX_TREE(dma_active_cacheline, GFP_NOWAIT);
static DEFINE_SPINLOCK(radix_lock);
@@ -497,10 +494,7 @@ static void active_cacheline_inc_overlap(phys_addr_t cln)
overlap = active_cacheline_set_overlap(cln, ++overlap);
/* If we overflowed the overlap counter then we're potentially
- * leaking dma-mappings. Otherwise, if maps and unmaps are
- * balanced then this overflow may cause false negatives in
- * debug_dma_assert_idle() as the cacheline may be marked idle
- * prematurely.
+ * leaking dma-mappings.
*/
WARN_ONCE(overlap > ACTIVE_CACHELINE_MAX_OVERLAP,
pr_fmt("exceeded %d overlapping mappings of cacheline %pa\n"),
@@ -555,44 +549,6 @@ static void active_cacheline_remove(struct dma_debug_entry *entry)
spin_unlock_irqrestore(&radix_lock, flags);
}
-/**
- * debug_dma_assert_idle() - assert that a page is not undergoing dma
- * @page: page to lookup in the dma_active_cacheline tree
- *
- * Place a call to this routine in cases where the cpu touching the page
- * before the dma completes (page is dma_unmapped) will lead to data
- * corruption.
- */
-void debug_dma_assert_idle(struct page *page)
-{
- struct dma_debug_entry *entry;
- unsigned long pfn;
- phys_addr_t cln;
-
- if (dma_debug_disabled())
- return;
-
- if (!page)
- return;
-
- pfn = page_to_pfn(page);
- cln = (phys_addr_t) pfn << CACHELINE_PER_PAGE_SHIFT;
-
- rcu_read_lock();
- if (!radix_tree_gang_lookup(&dma_active_cacheline, (void **) &entry,
- cln, 1) || entry->pfn != pfn)
- entry = NULL;
- rcu_read_unlock();
-
- if (!entry)
- return;
-
- cln = to_cacheline_number(entry);
- err_printk(entry->dev, entry,
- "cpu touching an active dma mapped cacheline [cln=%pa]\n",
- &cln);
-}
-
/*
* Wrapper function for adding an entry to the hash.
* This function takes care of locking itself.